Methods and systems for accessing and retrieving thrombo-emboli

ABSTRACT

The distal tip of a sensing catheter is placed in proximity to a target intravascular foreign material. A signal is propagated from the sensing catheter, a return signal is received, and at least a portion of the foreign material is captured and removed when the return signal is indicative of a foreign material located within a capture zone.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 62/950,058, filed Dec. 18, 2019 and U.S. Provisional Patent Application No. 63/064,273, filed Aug. 11, 2020, the entirety of each of which is hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

Thrombotic restrictions and occlusions within a patient's blood vessels are a significant medical problem and often require intervention to remove these restrictions and blockages to restore health to patients. While applicable to a wide range of vascular applications, the following background illuminates the problems through the example of patients suffering with Pulmonary Embolisms.

Venous thromboembolic disease (VTE) is a worldwide crisis. There are over 10 million cases of deep vein thrombosis (DVT) and pulmonary embolism (PE) diagnosed globally per year, with 1 million cases occurring in the United States and over 700,000 in France, Italy, Germany, Spain, Sweden, and the United Kingdom combined each year. There are approximately 60,000 to 100,000 deaths from PE in the United States each year. DVT and PE are part of the same continuum of disease, with over 95% of emboli originating in the lower extremities. When PE occurs, the severity depends on the embolic burden and its effect on the right ventricle as well as underlying cardiopulmonary comorbidities. Death can result from the acute increase in pulmonary artery (PA) pressure with increased right ventricular (RV) afterload and dysfunction.

Patients with high-risk pulmonary embolism (PE) were treated primarily with thrombolytic therapy delivered systemically or more locally through Catheter Directed Thrombolytics. These approaches result in multiple catheterization lab visits, lengthy hospital stays and often lead to bleeding complications. Newer approaches to PE treatment include single session thrombectomy treatments without the use of thrombolytics. These thrombectomy treatments include delivering a catheter into the PA to remove the thrombus through aspiration, and secondary tools may also macerate or disrupt the thrombus prior to aspiration. While thrombectomy results in fewer bleeding complications and reduced hospital stays compared to thrombolytics, there is much to be improved upon given the challenges of the procedure itself, including the ability to capture a broad spectrum of thrombus types and reduce the total volume of blood loss during the procedure.

The thrombectomy catheter is introduced through an introducer puncture in a large diameter vein. A flexible guide wire is passed through the introducer into the vein and the introducer is removed. The flexible guidewire provides a rail for a flexible guide catheter to be advanced through the right atrium into the right ventricle and into the pulmonary artery. The flexible guidewire is removed and replaced with a stiff guidewire. The large diameter thrombectomy catheter with support dilator is then advanced over the stiff guidewire to the pulmonary artery and the dilator is removed. If the large diameter thrombectomy catheter is not successful in accessing or aspirating thrombus in a more distal portion of the vessel, a smaller diameter catheter may be inserted through the large diameter catheter. This procedure, with multiple accessory devices and exchanges, is expensive, requires advanced catheter skills, results in a high volume of blood loss, and may not result in optimal patient outcomes.

SUMMARY

There is provided in accordance with one aspect of the invention, a system for advancing a large bore catheter to a remote site, such as a central pulmonary artery. The system comprises an elongate, flexible tubular catheter, having a proximal end, a distal end and a catheter hub on the proximal end, and an elongate, flexible rail, having a proximal end, a distal advance segment having a distal end and a rail hub on the proximal end. The distal end of the rail extends at least about 5 cm or 10 cm or 15 cm or more beyond the distal end of the catheter when the catheter hub is adjacent the rail hub.

The system may further comprise an engagement structure on the catheter hub, configured to releasably engage a complementary engagement structure on the rail hub. The rail may increase in flexibility in a distal direction, and may include a guidewire lumen. The guidewire lumen may be configured to accommodate a guidewire having a diameter of no greater than about 0.035″ and the rail has an outside diameter of no greater than about 0.025″ smaller than the inside diameter of the aspiration catheter. The catheter hub may comprise a hemostasis valve.

The wall thickness of the rail may be at least about 0.05 inches, or at least about 0.10 inches. The rail may comprise a proximal segment separated from the distal advance segment by a transition. The distal advance segment may have a greater flexibility than the proximal segment.

The access catheter may be at least about 8 French, or at least about 20 French. The access catheter hub may comprise a projection configured to snap fit into a complementary recess on the rail hub.

The system may further comprise a thrombus evacuation catheter configured to extend through the access catheter, and may comprise a thrombus engagement tool configured to extend through the thrombus evacuation catheter. The thrombus engagement tool may comprise an elongate flexible body having a thrombus engagement tip with a helical thread. The thread may extend from about two to about 10 revolutions around the elongate flexible body. The thread may have a maximum diameter that is no more than about 60% of an inside diameter of an adjacent portion of the thrombus evacuation catheter. The thrombus engagement tool may further comprise a handle on the proximal end, configured to permit manual rotation of the thrombus engagement tool.

In accordance with another aspect of the invention there is provided a method of advancing a catheter to a target vascular site. The method comprises the steps of providing a catheter having a guiding rail extending therethrough, the catheter having a catheter distal end and the rail having a rail distal end. With the rail distal end positioned at least about 10 cm distal to the catheter distal end, advancing the rail distal end to the target vascular site; and thereafter advancing the catheter along the guiding rail to the target vascular site. The advancing the rail step may be accomplished by advancing the rail over a guidewire. The advancing the rail step may be accomplished while the rail distal end is at least about 10 cm distal to the catheter distal end. The method may further comprise the step of unlocking the catheter from the guiding rail prior to the advancing the catheter along the guiding rail step.

The advancing the rail distal end step may comprise advancing the rail distal end from the vena cava through the tricuspid and pulmonary valves of the heart into the central pulmonary artery while the distal end of the catheter remains in the vena cava. The advancing the catheter step may comprise advancing the catheter distal end from the vena cava through the tricuspid and pulmonary valves of the heart into the central pulmonary artery over the guiding rail, following locating the distal end of the rail in the central pulmonary artery.

The advancing the rail distal end step may comprise advancing the rail distal end from the vena cava through the tricuspid valve before advancing the catheter along the rail.

The advancing the catheter step may be accomplished over a guidewire, and may be accomplished with a guidewire extending through a cannulation in the rail, or may be accomplished with a guidewire extending through the catheter. The catheter may be at least about 8 French, or at least about 24 French, and the rail may substantially fill (e.g., at least about 80% or 90% or more of the cross section of) the catheter lumen.

The advancing the rail distal end step may comprise advancing the rail distal end through at least one valve before advancing the catheter along the rail and through the valve. The advancing the rail distal end step may comprises advancing the rail distal end through a vascular obstruction before advancing the catheter along the rail and through the obstruction. The advancing the rail distal end step may comprise advancing the rail distal end through a tissue aperture before advancing the catheter along the rail and through the aperture.

The method may further comprise the step of removing the rail following the advancing the catheter step, and may further comprise the step of advancing a clot evacuation catheter through the lumen to the target vascular site. The method may further comprise the step of applying vacuum to the clot evacuation catheter, and may further comprise the step of advancing a thrombus engagement tool through the clot evacuation catheter. The thrombus engagement tool may be manually rotated to engage the thrombus.

In accordance with a further aspect of the invention, there is provided a method of removing a clot from a pulmonary artery to treat a pulmonary embolism. The method comprises the steps of providing a large bore catheter having a guiding rail extending therethrough, the large bore catheter having a large bore catheter distal end and the rail having a rail distal end. With the rail distal end at least about 15 cm distal to the large bore catheter distal end, the rail distal end is advanced from the vena cava through the tricuspid and pulmonary valves of the heart into the central pulmonary artery while the distal end of the large bore catheter remains in the vena cava. The large bore catheter is thereafter advanced distally over the rail until the large bore catheter distal end is at least as far as the central pulmonary artery. The rail is thereafter proximally removed from the large bore catheter, and at least a portion of a clot is drawn from a pulmonary artery into the large bore catheter. The drawing step may be accomplished using vacuum.

The method may further comprise the step of advancing a clot capture catheter through the large bore catheter following the proximally removing the rail step, and may further comprise the step of advancing a clot engagement tool through the clot capture catheter. The clot engagement tool may be manually rotated to engage the clot.

There is also provided a method of removing foreign material from the vascular system, comprising the steps of positioning the distal tip of a sensing catheter in proximity to a target foreign material; propagating a signal from the sensing catheter; receiving a return signal; and capturing and removing at least a portion of the foreign material when the return signal is indicative of a foreign material located within a capture zone. The capturing and removing steps may be accomplished by the sensing catheter. The method may further comprise removing the sensing catheter following the receiving a return signal step, and introducing a clot capture catheter to accomplish the capturing and removing steps.

The foreign material may be a clot, which may be in the venous system, such as a deep vein thrombosis or a pulmonary embolism.

The return signal may enable characterization of tissue within the capture zone, and may enable differentiation between clot and vessel wall within the capture zone. The propagating a signal step may comprise propagating an ultrasound signal or an electromagnetic signal such as in the UV-visible range. The electromagnetic signal may comprise multiple wavelengths.

The propagating a signal step may comprise propagating visible light through the sensing catheter and beyond the distal tip. The method may further comprise receiving the return signal using a sensor carried by the sensing catheter. A visible light pathway may be created through blood between the distal tip and the target foreign material. The step of creating a visible light pathway through blood between the distal tip and the target foreign material may comprise infusing an optically transparent medium to displace blood from the pathway. The method may further comprise the step of deploying a barrier to temporarily contain at least a portion of the optically transparent medium within the pathway. The barrier may be deployed from the sensing catheter or from the aspiration catheter.

The differentiation may be accomplished by a clinician, observing an image generated by the return signal. The differentiation may be accomplished by a processor configured to differentiate between return signals indicative of either a foreign material or a vessel wall. The processor may further be configured to generate an indicium in response to the differentiation between a foreign material and a vessel wall. The indicium may comprise an audio or visual signal. The sensing catheter may be axially reciprocally introduced through an access catheter. The method may further comprise the step of proximally retracting the sensing catheter through the access catheter following the receiving a return signal, and may further comprise the step of distally advancing a clot capture catheter through the access catheter and capturing and removing at least a portion of the foreign material using the clot capture catheter.

Any of the methods disclosed herein may further comprise the step of deflecting the tip laterally in response to detecting vessel wall within the capture zone, prior to the capturing and removing steps.

In accordance with a further aspect of the invention, there is provided a dual dilator access system, comprising a large diameter access catheter, having an elongate tubular body with a proximal end, a distal end and a central lumen extending axially therethrough. A small diameter catheter is axially movably slidable through the central lumen. A first dilator is extendable through the central lumen, in between the small diameter catheter and the large diameter catheter; and a second dilator extendable through the small diameter catheter. The large diameter catheter may be an aspiration catheter. The small diameter catheter may be a clot grabber catheter.

The system may further comprise a proximal coupling for interlocking the large diameter catheter and the small diameter catheter. The first dilator may have a tapered distal end. The large diameter access catheter may be at least about 14 French. The tapered distal end may be positionable beyond the distal end of the small diameter catheter. The clot grabber catheter may include a distal tip with a helical thread. The small diameter catheter may comprises an imaging catheter.

The first dilator may have a split line along which it can split for proximal retraction and removal. The split line may comprise a weakening in the wall or an axial scoring line.

The large diameter access catheter may comprise an inside surface defining the central lumen, and the inside surface comprises at least one surface discontinuity for influencing the behavior of material drawn into the central lumen. The surface discontinuity may comprise a ridge. A plurality of axially extending, circumferentially spaced apart ridges may be provided along at least a distal zone of the catheter. The distal zone may extend proximally from the distal end within the range of from about 1 to about 20 cm, and the discontinuity may extend all the way to the proximal end of the catheter. The ridge may be in a spiral configuration. The surface discontinuity may comprise at least one ramp and edge for permitting material to travel proximally in the central lumen and resisting distal travel of the material in the lumen. There may be a plurality of ramps which incline radially inwardly in the proximal direction and each terminate in a proximal edge. The central lumen may have a non circular transverse cross sectional configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic side elevational view of a thromboembolic imaging catheter.

FIG. 1B is a distal end view of the catheter of FIG. 1A.

FIG. 1C illustrates the catheter of FIG. 1A, extending through a lumen in an aspiration catheter.

FIG. 2A is a schematic side elevational view of a thromboembolic thermal sensing catheter.

FIG. 2B is a distal end view of the catheter of FIG. 2A.

FIG. 3A is a schematic side elevational view of a thromboembolic force sensing catheter.

FIG. 3B is a distal end view of the catheter of FIG. 3A.

FIG. 4A is a schematic side elevational view of a thromboembolic ultrasound catheter.

FIG. 4B is a distal end view of the catheter of FIG. 4A.

FIG. 5A is a schematic side elevational view of a thromboembolic electromagnetic spectrum imaging catheter.

FIG. 5B is a distal end view of the catheter of FIG. 5A.

FIG. 5C is a distal end view of a variation of the catheter of FIG. 5A.

FIG. 6 is a side elevational view of the components in a thromboembolic visualization and aspiration system.

FIG. 7A is a side elevational view of a catheter having an internal stop ring.

FIG. 7B is a longitudinal cross section through the catheter of FIG. 8A, and detail view of the stop ring.

FIG. 7C is a side elevational view of a thrombus engagement tool having a complementary limit for engaging the stop ring of FIGS. 7A and 7B.

FIG. 7D is a side elevational view of a distal portion of the thrombus engagement tool of FIG. 7C.

FIG. 7E is a longitudinal cross section through the thrombus engagement tool of FIG. 7D.

FIG. 7F is a perspective cut away view of a distal portion of the thrombus engagement tool of FIG. 7C.

FIG. 7G is a transverse cross section through a distal stopper carried by the thrombus engagement tool.

FIG. 7H is a transverse cross section through an alternative distal stopper.

FIGS. 8A-8C are side elevational and cross sectional views of tip profiles, showing proximal and distal tapers of the helical thread envelope.

FIG. 9 is an end elevational view of a helical tip having circumferentially varying major diameter creating a radially non-uniform separation from the catheter lumen wall.

FIG. 10 is an end perspective view of a cannulated helical tip element with a lumen for a guidewire or other devices or infusion or aspiration of fluids.

FIG. 11 is a schematic side elevational view of an over the wire helical tipped structure.

FIG. 12 is a schematic side elevational view of a helical tipped structure with a fixed guide wire tip.

FIG. 13 is a side elevational view of a large bore catheter.

FIG. 14 is a side elevational partial cross section of the catheter of FIG. 13, having a cannulated guide rail extending therethrough over a guidewire.

FIG. 15 is a cross sectional view through a dual dilator system such as that shown in FIG. 16.

FIG. 16 is a side elevational cross section of a distal portion of a dual dilator system of the present invention.

FIG. 17 is a cross section as in FIG. 16, with a distal tip formed by the tubular dilator.

FIG. 18 is a side elevational view of a portion of a tubular dilator having a separation line to allow longitudinal splitting of the sidewall during proximal retraction from the system.

FIG. 19A is a longitudinal cross-sectional view through a distal zone of a catheter, having axially extending surface structures on the inside surface of the catheter wall.

FIG. 19B is a longitudinal cross-sectional view as in FIG. 19A, having helical surface structures on the inside surface of the catheter wall.

FIG. 20 illustrates transverse cross-sectional views through the catheter of FIG. 19A, showing different ridge and groove configurations.

FIG. 21 illustrates an inside surface of a catheter wall having differential friction surface structures for facilitating proximal movement of thrombus and inhibiting distal movement of thrombus.

FIG. 22 shows an angled distal catheter tip.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The devices and systems of the present invention include catheter-based technology that enables accessing and retrieving a vascular obstruction. In some implementations of the system, a separate facilitator maybe provided for advancing through an aspiration catheter to facilitate engagement of the obstruction. In other implementations of the system, sensors are provided which provide the clinician with information about the presence, amount, and characteristics of tissue in front of the catheter. This enables valuable diagnostic information such as the identity of tissue within a clot capture zone adjacent and beyond the distal tip of the catheter, e.g., whether the catheter is aimed at clot or at the vessel wall, and potentially assists in developing an appropriate treatment strategy. As used herein, terms like clot, thrombus, embolization, foreign matter and the like will be considered synonymous unless otherwise described.

For instance, when planning to remove a pulmonary embolism from a pulmonary artery, it may be valuable to differentiate thrombus from vascular tissue and confirm 1) the presence and location of the thrombus, 2) the size and shape of the thrombus, and 3) the morphology and composition of the thrombus. All of these can be accomplished utilizing the single, low profile catheter in accordance with the present invention. The present sensing catheter described in further detail below includes, but is not limited to one or more sensors of the following modalities: CMOS imaging (or CCD) to enable visualization; thermal sensing; force sensing; ultrasound imaging; infrared imaging; spectroscopy tomography; or electrochemical sensing.

The sensing catheter is thus enabled to provide clinical data of the following types: Location of target obstruction; thrombus versus tissue wall; size and shape; mechanical properties like hardness/stiffness; temperature differences; or morphology/age.

Although primarily described in the context of a pulmonary artery embolectomy catheter with a target tissue characterization feature, catheters of the present invention can readily be adapted for use in removal of deep vein thrombosis or other vascular (e.g., neurovascular, other peripheral vascular, coronary), emboli or obstructions as will be understood in the art. Any of the devices disclosed herein can also be modified to incorporate additional structures, such as clot grabbing and retrieval features, partial length or full length guidewire lumen for over the wire or rapid exchange guidance, permanent or removable column strength enhancing mandrels, two or more lumens such as to permit drug, contrast or irrigant or optical field clearing infusion or to supply inflation media to an inflatable balloon carried by the catheter.

Any of the catheters disclosed herein may have a deflectable or preshaped curved or angled distal steering zone. At least one and optionally two or three or more pull wires may axially extend through corresponding pull wire lumen(s), to enable lateral deflection of the distal tip of the catheter. A single pull wire can provide deflection in a single direction and plane, to cooperate with rotation of the catheter to achieve 360 degree maneuverability. Two or three or more pull wires, typically spaced equidistantly around the circumference of the catheter body, enable greater steerability without the need for catheter rotation. Deflection or preshaped curvature or angulation of the distal tip enables redirection of the tissue capture zone away from a first target tissue (e.g., healthy vessel wall) to a second target tissue (e.g., a clot). Catheters of the present invention can include any combination of the foregoing features, depending upon the intended clinical application and desired functionality as will be readily apparent to one of skill in the art in view of the disclosure herein.

In addition, the present invention will be described primarily in the context of removing obstructive material from the pulmonary artery but may have applicability for use throughout the body wherever it may be desirable to characterize a target tissue to support a clinical decision to remove or treat a first target tissue or redirect the catheter to a different, second target tissue. For example, sensing catheter shafts in accordance with the present invention may be dimensioned for use throughout the coronary, peripheral, and neurovasculature, both arterial and venous, the gastrointestinal tract, the urethra, ureters, Fallopian tubes and other lumens and potential lumens, as well. The sensing catheter of the present invention may also be used to provide minimally invasive percutaneous tissue access, such as for diagnostic or therapeutic access to a solid tissue target (e.g., breast or liver or brain biopsy or tissue excision), access to bones such as the spine for surface characterization and other applications.

Referring to FIGS. 1A and 1B, a sensing catheter generally comprises an elongated flexible tubular body 10 extending between a proximal end 12 and a distal functional end 14. The length of the tubular body depends upon the desired application. For example, catheter lengths from about 120 cm to about 150 cm or more are typical for use in femoral access percutaneous transluminal coronary applications. Intracranial or other applications may call for a different catheter shaft length depending upon the vascular access site, as will be understood in the art.

In certain embodiments intended to treat pulmonary embolism via a femoral vein access site, the catheter 10 will generally have an axial length within the range of from about 80 cm to about 110 cm for a primary treatment catheter and from about 130 cm to about 150 cm for a secondary catheter intended to advance through a primary catheter. Outside diameters may be within the range of from about 8 F to about 32 F depending upon the procedure and intended clinical performance.

The distal end 14 of catheter 10 is provided with at least one sensor 16 for characterizing the clot, vessel wall, or other target tissue. In an embodiment intended for optical visualization, an optical sensor such as a CMOS or CCD chip may be located at the distal end of the catheter, or in a proximal handpiece or module, and optically coupled to a fiber optic element extending axially throughout the length of the catheter. A light source such as an LED is also provided, either at the distal end of the catheter, or at the proximal end of the catheter and optically coupled to a fiber optic light guide extending through the catheter body.

The catheter 10 may additionally be provided with a guide wire lumen 17 extending between a guide wire port on the distal end 14 of the catheter 10 and a proximal guide wire port. The proximal guide wire port may be through a sidewall of the catheter 10 in a rapid exchange implementation, or may be provided on the hub 27 in an over the wire configuration. One or two or more additional ports or electrical connectors may be provided on the proximal hub 27, depending upon the functionality of the catheter.

The catheter is provided with at least one infusion lumen 18, and two in the illustrated embodiment, extending from a proximal infusion port 22 on a proximal hub 27 to a corresponding exit port on the distal end 14 of the catheter. A deflection mechanism may be provided, for laterally deflecting a distal steering zone on the catheter 10. In one implementation, a pull wire lumen 19 extends from a proximal deflection control (not illustrated) carried by the hub 27 and extending distally to the deflection mechanism. The proximal control may comprise a rotatable control such as a ring that may be rotatable about the longitudinal axis of the catheter, or a rotatable knob, a slider switch, or other suitable control for placing a control wire under tension or compression. The deflection mechanism may form a deflection zone on a distal portion of the catheter 10, in which an axial length of the catheter sidewall is provided on a first side with a plurality of transverse slots, leaving an opposing spine side with relatively higher column strength. The deflection wire may be attached to the side wall distally of the slots. Proximal retraction of the deflection wire causes axial compression of the slotted side of the tubular body thereby deflecting the axis away from the spine side and towards the slotted side of the tubular body.

In use, a fluid media, optically transparent in the visible range (e.g., water or saline) is infused from a source 33 and through lumen 18 to displace blood in a visualization and capture zone 21 in front of the catheter and create an optical path between the sensor and target tissue. A temporary barrier such as a hood 20 may be desirable to lengthen the dwell time of the optically transmissive media within the optical path, before it is replaced with blood and become optically opaque in the visual range.

In the illustrated embodiment, the barrier is in the form of an imaging hood 20 such as a self expandable cone, to protect the viewing area from blood flow. The barrier is carried by the distal end of the sensing catheter and may be self expanding upon release from a restraint such as the outer access catheter which may also be an aspiration catheter.

Alternatively, referring to FIG. 1C, the imaging hood 20 or other barrier may be carried by the aspiration catheter 26. In this implementation, the sensing catheter 10 may be advanced distally through a lumen 24 in the aspiration catheter 22, and the imaging hood 20 utilized as described to facilitate establishment of an optical path between the sensor and target tissue. The ID of the lumen 24 may be at least about 0.005″ and in some implementations at least about 0.010″ or 0.015″ or more greater than the OD of the imaging catheter 10 to provide an aspiration lumen while the imaging catheter 10 is in place, and also accommodate a guidewire 28.

Following confirmation by the sensing catheter 10 that the aspiration catheter 26 is positioned at the desired site, the sensing catheter 10 may be proximally retracted and the central lumen 24 can be used for direct aspiration or to receive a clot capture catheter (discussed below) therethrough. At this point, the imaging hood 20 can perform the additional and distinct function of helping advance the clot proximally into the aspiration catheter.

Image data from the image sensor is carried proximally through the catheter by one or more conductors, to a connector 30, and via cable 32 into a processor 25 for converting into a visual image or other visual and/or audible indicium of characterization of the target tissue. The image can be displayed on a conventional display such as a laptop, tablet, wall hung display or wearable display.

As an alternative to direct visualization in the visible light range, a variety of other characterizing modalities may be used to characterize target tissue. For example, referring to FIGS. 2A-2B, in a given environment, the foreign material and healthy wall may have different surface temperatures. In this situation, a thermal sensing catheter 34 may be provided with one or two or more distal temperature sensors 36. Intravascular thermal sensors are described, for example, in U.S. Pat. No. 9,420,955 entitled “Intravascular temperature Monitoring System and Method”, the disclosure of which is hereby incorporated by reference in its entirety herein.

Alternatively, hemoglobin reflectivity measurement and optional simultaneous optical coherence tomography imaging capabilities may be added to the catheter, as described in US published patent application No. 2011/0077528 to Kemp et al, entitled Method and Apparatus for Simultaneous Hemoglobin Reflectivity Measurement and OCT Measurement, Thrombus Detection and Treatment, and OCT Flushing, published Mar. 31, 2011, which is hereby incorporated in its entirety herein by reference. Hemoglobin reflectivity measurement enables differentiation between ‘red’ thrombus and ‘white’ thrombus, which differ largely in the concentration of red blood cells.

Alternatively, a chemistry-based sensor may be used which uses the chemical compostion of the tissue to create a signal which can differentiate between the foreign body and non-target tissue, or characterize different tissue types. For example, Fibrinogen has been reported to have been detected using an electrochemical impedance biosensor (EIB) formed by draping an erythrocyte membrane (EM) configured for the detection of fibrinogen. Measurements with the FIB may reveal that the specific (selective) adsorption of fibrinogen onto the EM causes a clear rise in the value of interfacial charge transfer resistance. The sensing ability of the EIB for fibrinogen detection may show a wide linear range from 0.0001 to 5 mg/mL, with a limit of detection of 49 ng/mL (144 pM).

Preferably the sensors in general detect a relatively high level of hemoglobin, or fibrinogen, or prothrombin, or other clotting pathway factors which would not be as abundant in vascular wall tissues.

The clot and native vessel wall may also vary in physical properties such as compressibility or hardness. Referring to FIGS. 3A-3B, this may be measured by one or two or more force, pressure, or displacement sensors 28 carried by the distal end 14 of a force sensing catheter 40.

In certain embodiments it may be desirable to interrogate tissue within the capture zone with a first signal, and then capture reflected or rebounded signal for comparison to characterize the target tissue. For example, referring to FIGS. 4A-4B, unitrasound catheter 44 may be provided with ultrasound transmitter and receiver chips 46 which may be carried by the catheter 44 to interrogate tissue in the capture zone.

Depending upon the nature of the target tissue and adjacent healthy tissue, any of a variety of other signals in the electromagnetic spectrum may be propagated from an EMS imaging catheter 50 with reflected signal captured by the catheter to identify and define matter in front of catheter. See, e.g. FIGS. 5A-5C.

EMS imaging catheter 50 may comprise one or two or more transmitters 52 for transmitting EMS imaging signals to target tissue and one or two or more receivers 53 for sensing reflected EMS signals. Aspiration lumen 54 may be provided, if aspiration is desired. One or more working channels or delivery channels 56 may be provided, depending upon the desired functionality.

The number and orientation of lumen, electrical conductors and other structures within the catheter body can be varied widely depending upon the desired functionality of the catheter. For example, FIG. 5C illustrates an alternate configuration for the catheter of FIG. 5 A, in which a guide wire lumen 17 has been provided along with a pull wire lumen 19 in a steerable implementation. An EMS sensor or sensor/receiver array 58 may be provided, along with one or two fluid lumen 18 such as for the delivery of saline and/or drug delivery and/or aspiration.

Intravascular sensing systems that may be adapted into the catheters of the present invention for characterizing material within the capture zone 21 as native vascular wall or foreign material are disclosed, for example, in U.S. Pat. No. 10,534,129, issued Jan. 14, 2020 and entitled “System and method providing intracoronary laser speckle imaging for the detection of vulnerable plaque”; U.S. Pat. No. 7,473,230, issued Jan. 6, 2009 and entitled “Instrumented catheter with distance compensation to sense vulnerable plaque”; and U.S. Pat. No. 7,450,241, issued Nov. 11, 2008 and entitles “Detecting vulnerable plaque”, the disclosures of which are hereby incorporated in their entireties herein by reference.

In general, the distal end 14 of the sensing catheter 10 may be provided with at least one signal transmitting surface and at least one signal receiving surface. The transmitting surface is adapted to transmit a signal from the distal end of the catheter and generally in the distal direction with respect to the longitudinal axis of the catheter. The receiving surface is adapted for receiving a reflected return signal with at least a component of the signal traveling in a generally proximal direction with respect to the distal end of the catheter. In one embodiment, the transmitting surface comprises the distal end of a fiber optic or fiber optic bundle, a distal light source, or a transparent window which may be a lens positioned at the distal end of a fiber optic or fiber optic bundle or distal light source. Similarly, the receiving surface may comprise a distal end of a receiving fiber optic or a distal sensor, a transparent window which may be a lens positioned distally of the receiving fiber optic or sensor. In one embodiment, two transmitting surfaces and two receiving surfaces may be provided each communicating with a spectrometer via unique communication lines.

Electrical signals from the sensors may be transmitted to a spectrometer or other device suitable for the sensed signal, which remains outside of the patient. The construction and use of spectrometers such as to measure RGB and other UV, visible and IR wavelengths is well understood in the pulse oximetry art, among others, and will not be disclosed in detail herein. In general, a transmitter/detector may be able to transmit multiple wavelengths of light, which propagate beyond the transmit surface and into a target beyond the distal end of the sensing catheter. Some of the transmitted light is absorbed in the target, while other transmitted light is reflected back and received at the receiving surface. The reflected light is thereafter propagated for processing. The optical absorption/reflection characteristics of the clot compared to healthy vessel wall enable differentiation of the target tissue types.

Any of the foregoing sensing catheters may be utilized in the image-guided PE or DVT thrombectomy system and procedure in accordance with the present invention.

Referring to FIG. 6, the system for accessing and retrieving thrombo-emboli in accordance with the present invention generally comprises an access catheter 40 such as a large bore (e.g. 24 Fr) catheter, an aspiration or evacuation catheter 62, optionally an imaging functionality, which may be a separate sensing catheter 64, and a clot retrieval tool 66 configured to be extendable through the evacuation catheter 62.

One example of the method and use of the system is described below.

-   -   Femoral vein or internal jugular vein access is achieved using         conventional techniques.     -   An access catheter 60 such as a 24 Fr catheter is advanced         through the right heart chambers and into the Pulmonary Artery.

Aspiration may be applied to the access catheter for clot removal in the proximal pulmonary artery. If that fails, a mechanical facilitator device such as clot retrieval tool 66 may be advanced through the access catheter 60 to assist with clot removal. If that fails, the evacuation catheter 62 may be advanced through the 24 Fr access catheter 40 and advanced to the thrombus.

If desired, the imaging catheter 64 may be advanced through the evacuation catheter 62 to identify and verify thrombus. Alternatively, when the imaging and evacuation catheters have been integrated, only one catheter with both imaging elements and an evacuation lumen would need to be advanced through the 24 Fr access catheter 40 at this stage.

Aspiration is turned on to hold thrombus in place at the evacuation collection funnel 20 while exchanging Imaging Catheter 64 for the clot retrieval catheter 62.

The thrombus engagement tool 66 may be advanced into the thrombus for thrombus engagement.

The thrombus engagement tool 66, evacuation catheter 62 and engaged thrombus are proximally retracted through the 24 Fr catheter 60. Retraction may be accomplished under optional aspiration to maintain attachment of the thrombus.

Optionally, the imaging catheter 64 may be reintroduced to confirm target thrombus removal and identify additional thrombus to remove.

Aspiration, exchange, engage, extract, re-image may be repeated as desired.

Following aspiration, all catheters may be removed.

Additional details of the devices useful in the methods and systems of the present invention are discussed below.

Referring to FIGS. 7A and 7B, any of the aspiration catheters disclosed herein may be provided with an axial restraint for cooperating with a complementary stopper on a thrombus engagement tool 2401 (FIG. 7C) to permit rotation of the thrombus engagement tool 2401 but limit the distal axial range of travel of the thrombus engagement tool 2401.

The method of limiting distal advance of the core wire and helical tip element may be achieved by a limit attached to the core wire or torque member in sliding contact with an internal stop as described above, or in sliding contact with a stop surface carried on any of a variety of accessories or devices attached to the proximal end of the catheter in which the helical member assembly is contained. This includes a Tuohey-Borst or other hemostasis valve accessory.

In the illustrated implementation, the restraint comprises at least one projection extending radially inwardly through the sidewall or from the inside surface of the tubular body, configured to restrict the inside diameter of the aspiration lumen and engage a distal face carried by the thrombus engagement tool. The restraint may comprise one or two or three or four or more projections such as tabs, or, as illustrated, may comprise an annular ring providing a continuous annular proximally facing restraint surface. In the illustrated implementation, the restraint is positioned in a distal location in the catheter e.g., within about 20 cm or 10 cm or less from the distal end. This allows precise positioning of the distal thrombus engagement tool tip with respect to the distal end of the catheter, decoupled from bending of the catheter shaft, and prevent the distal tip from extending beyond a preset position such as the distal end of the catheter.

In other implementations, the restraint may be located at the proximal end of the catheter such as at the proximal hub, or even external to the catheter, such as on the proximal end of the hub. For example, the thrombus engagement tool 66 may be provided with a handle 70 as illustrated in FIG. 6. Handle 70 comprise an axially elongate body 72 configured to be twirled about its longitudinal axis between two or three fingers of a single hand. Surface friction enhancing structures such as a plurality of axially extending flats or ridges 74 may be provided on an exterior surface of the body 72. Distal end 76 may be configured to rotatably slide against a proximal surface 78 on the hub 27 for evacuation catheter 62.

In certain clinical applications, it may be desirable for the helical tip to be able to advance beyond the tip of the surrounding catheter, thus an axial limit system may be omitted, or may be configured to permit the desired axial orientation. For example, distal extension of the distal end of the helical tip beyond the distal end of the catheter may be limited to no more than about 5 mm or 3 mm or 1.5 mm or 1.0 mm or less.

The limit on distal advance of the helical tip may include a first configuration in which distal advance is limited to a first position proximate the distal end of the evacuation catheter to prevent injury to the vascular wall. Upon a user initiated adjustment, the helical tip may be advanced to a second position out of the distal end of the catheter for inspection and cleaning purposes. This adjustment of the limiting mechanism may be locked out following cleaning or inspection, to limit distal travel to the first position to prevent an undesired degree of exposure of the helical tip element when the system is within the patient's vasculature.

In the illustrated embodiment, the restraint may be a metal (e.g., nitinol, stainless steel, aluminum, etc.) circular band or ring or protrusion 2402 mounted on or built into a sidewall 2403 of the catheter near the proximal hub, on the proximal hub on the proximal end of the catheter shaft or near the distal tip. The restriction element 2402 extends into the ID of the catheter. Further, the restriction element 2402 may be radiopaque for visibility under fluoroscopy. The restriction element 2402 carries a proximally facing surface 2405 for example an annular circumferential bearing surface that extends into the inner diameter of the catheter to provide a sliding interface with a stopper such as distal stopper 2414 (FIG. 7C) on the rotating core assembly. For example, the stopper 2414 may be a radially outwardly extending feature on the rotating assembly which interfaces with the restriction element 2402 of the catheter to permit rotation but limit the distal advancement and prevent distal tip displacement beyond a desired relationship with the catheter distal tip.

In one implementation, in its relaxed form prior to securing within the catheter lumen, the ring 2402 is a C-shaped or cylinder shaped with an axially extending slit to form a split ring. The ring 2402 is compressed using a fixture that collapses the ring to a closed circle shape, allowing it to slide inside the (e.g., 0.071″) catheter. When the ring is released from the fixture, the ring expands radially to the largest diameter permitted by the inside diameter of the catheter. The radial force of the ring engages the insider surface of the catheter and resists axial displacement under the intended use applied forces. In another implementation, the ring is a fully closed, continuous annular structure (like a typical marker band) and its distal end is slightly flared in a radially outwardly direction to create a locking edge. The ring is inserted into the catheter from the distal end. The flared section with the locking edge keeps the ring in place when axial force is applied from the proximal side.

Referring to FIGS. 7D and 7F, distal segment 2407 of the rotatable core wire comprises a torque coil 2412 surrounding a core wire 2410. The illustrated torque coil 2412 comprises an outer coil 2413 concentrically surrounding an inner coil 2415 having windings in opposite directions.

Alternatively, for an over-the-wire embodiment (e.g., FIG. 11) alternative torqueable structures may be utilized, including a polymeric tube with an embedded metallic wire braid intended to be entirely inserted over and rotated around a central guidewire. Additionally, the geometry of the lumen of the torqueing member may minimize the space between the lumen inner diameter and the guidewire so as to minimize fluid or airflow and virtually eliminate blood flow out of the lumen under biologically typical pressures or air leakage to significantly reduce vacuum pressures when a vacuum pump is used to create a vacuum through the aspiration catheter (60) near the distal end of the elongate structure.

Although the coil 2412 is shown in FIGS. 7D, 7E and 7F as having a constant diameter, this leaves an internal entrapped space between the coil and the core wire, as a result of the tapering core wire 2410. When the area of the aspiration lumen between the coil and the inside wall of the corresponding catheter is optimally maximized, the diameter of the coil 2412 can taper smaller in the distal direction to track the taper of the core wire. This may be accomplished by winding the coil onto the core wire which functions as a tapered mandrel, or using other techniques known in the art. In this execution, the OD of the core wire tapers smaller in the distal direction, while the area of the aspiration lumen tapers larger in the distal direction.

As illustrated further in FIGS. 7D and 7E, the torque coil 2412 extends between a proximal end 2430 and a distal end 2432. The proximal end 430 is secured to a tapered portion of the core wire 2410. As illustrated in FIG. 7E, the core wire 2410 tapers from a larger diameter in a proximal zone to a smaller diameter in a distal zone 2434 with a distal transition 436 between the tapered section and the distal zone 2434 which may have a substantially constant diameter throughout. The inside diameter of the inner coil 2415 is complementary to (approximately the same as) the outside diameter at the proximal end 2430 of the core wire 2410. The tapered section of the core wire 2410 extends proximally from the distal transition 436 to a proximal transition (not illustrated) proximal to which the core wire 2410 has a constant diameter.

The torque coil 2412 may additionally be provided with a proximal radiopaque marker and/or connector such as a solder joint 2438. In the illustrated implementation, the proximal connector 2438 is in the form of an annular silver solder band, surrounding the inner coil 2415 and abutting a proximal end of the outer coil 2413.

The axial length of the torque coil 2412 may be within the range of from about 10 mm to about 50 mm and in some embodiments within the range of from about 20 mm to about 40 mm. The distal transition 2436 may be positioned within the range of from about 5 mm to about 20 mm and in some implementations within the range of from about 8 mm to about 12 mm from the proximal end of the distal cap 2420.

Referring to FIGS. 7E and 7F, the distal stopper 2414 may be provided with one or two or three or more spokes 440, extending radially outwardly from the outer coil 2413, and optionally supported by an annular hub 442 carried by the torque coil 2412. The spoke 440 may support a slider 441 having a peripheral surface 443, configured for a sliding fit within the inside diameter of the delivery catheter lumen. Preferably at least three or four or five or more spokes 440 are provided, circumferentially spaced apart equidistantly to provide rotational balance. In the illustrated embodiment, three spokes 440 are provided, spaced at approximately 120° intervals around the circumference of the torque coil 2412.

The distal stopper 2414 carries a plurality of distal surfaces 446, such as on the slider 441. The distal surface 446 is configured to slidably engage a proximal surface of a stop on the inside diameter of the delivery catheter, such as a proximally facing surface 2405 on a radially inwardly extending annular flange or ring 2402. See FIG. 7B discussed previously. This creates an interference fit with a bearing surface so that the distal stopper 2414 can rotate within the delivery catheter, and travel in an axial distal direction no farther than when distal surface 446 slideably engages the proximal surface 2405 on the stop ring 2402.

Referring to FIG. 7E, the distal end 432 of the torque coil 2412 is provided with a distal cap 2420. Distal cap 2420 may comprise an annular band such as a radiopaque marker band, bonded to the outside surface of the inner coil 2415, and axially distally adjacent or overlapping a distal end of the outer coil 2413. A proximally extending attachment such as an annular flange 2417 may be provided on the thrombus engagement tool tip 2416, for bonding to the distal cap 2420 and in the illustrated embodiment to the outer coil 2413. The distal cap 2420 may also be directly or indirectly bonded to a distal end of the core wire 2410.

The thrombus engagement tool tip 2416 is provided with a distal end 450, and a clot engagement element such as a plurality of proximally and/or radially facing engagement surfaces. In the illustrated implementation, the clot engagement element comprises a helical flange 452 that increases in diameter in the proximal direction. The flange may extend at least about one full revolution and generally less than about five or four or three revolutions about an extension of the longitudinal axis of the core wire 2410. The helical flange may be provided with a rounded, blunt edge 454, configured for slidably rotating within the tubular delivery catheter. Additional tip configurations are discussed in connection with FIGS. 8 and 9, below.

The maximum OD for the tip 2416 is generally at least about 0.005 inches and preferably at least about 0.01 inches or 0.015 inches or more smaller than the ID of the catheter aspiration lumen through which the embolism treatment system 2401 is intended to advance, measured at the axial operating location of the tip 2416 when the stopper 2414 is engaged with the stop ring. For example, a tip having a maximum OD in the range of from about 0.050-0.056 inches will be positioned within a catheter having a distal ID within the range of from about 0.068 to about 0.073 inches, and in one embodiment about 0.071 inches. With the tip centered in the lumen of the delivery (aspiration) catheter, the tip is spaced from the inside wall of the catheter by a distance in all directions of at least about 0.005 inches and in some embodiments at least about 0.007 inches or 0.010 inches or more.

Thus an unimpeded flow path is created in the annular (if centered) space between the maximum OD of the tip, and the ID of the catheter lumen. This annular flow path cooperates with the vacuum and helical tip to grab and pull obstructive material into the catheter under rotation and vacuum. The annular flow path is significantly greater than any flow path created by manufacturing tolerances in a tip configured to shear embolic material between the tip and the catheter wall.

Additional aspiration volume is obtained as a result of the helical channel defined between each two adjacent threads of the tip. A cross sectional area of the helical flow path of a tip having a maximum OD in the range of from about 0.050 to about 0.056 inches will generally be at least about 0.0003 square inches, and in some embodiments at least about 0.00035 or at least about 0.000375 inches. The total aspiration flow path across the helical tip is therefore the sum of the helical flow path through the tip and the annular flow path defined between the OD of the tip and the ID of the catheter lumen.

The combination of a rounded edge 454 on the thread 452 and space between the thread 452 and catheter inside wall enables aspiration both through the helical channel formed between adjacent helical threads as well as around the outside of the tip 2416 such that the assembly is configured for engaging and capturing embolic material but not shearing it between a sharp edge and the inside wall of the catheter. The axial length of the tip 2416 including the attachment sleeve 2417 is generally less than about 6 mm, and preferably less than about 4 mm or 3 mm or 2.5 mm or less depending upon desired performance.

The pitch of the thread 452 may vary generally within the range of from about 25 degrees to about 80 degrees, depending upon desired performance. Thread pitches within the range of from about 40-50 degrees may work best for hard clots, while pitches within the range of from about 50 to 70 degrees may work best for soft clots. For some implementations the pitch will be within the range of from about 40-65 degrees or about 40-50 degrees.

The tip 2416 may additionally be provided with a feature for attracting and/or enhancing adhesion of the clot to the tip. For example, a texture such as a microporous, microparticulate, nanoporous or nanoparticulate surface may be provided on the tip, either by treating the material of the tip or applying a coating. A coating of a clot attracting moiety such as a polymer or drug may be applied to the surface of the tip. For example, a roughened Polyurathane (Tecothane, Tecoflex) coating may be applied to the surface of at least the threads and optionally to the entire tip. The polyurethane may desirably be roughened such as by a solvent treatment after coating, and adhesion of the coating to the tip may be enhanced by roughening the surface of the tip prior to coating. The entire tip may comprise a homogeneous construct of any of the materials described above, or other polymeric materials, rather than just the coating.

Alternatively, the core wire 2410 may be provided with an insulating coating to allow propagation of a negative electric charge to be delivered to the tip to attract thrombus. Two conductors may extend throughout the length of the body, such as in a coaxial configuration, or a single conductor and an external grounding electrode may be used. Energy parameters and considerations are disclosed in U.S. Pat. No. 10,028,782 to Orion and US patent publication No. 2018/0116717 to Taff et al., the disclosures of each of which are hereby expressly incorporated by reference in their entireties herein. As a further alternative, the tip 2416 can be cooled to cryogenic temperatures to produce a small frozen adhesion between the tip and the thrombus. Considerations for forming small cryogenic tips for intravascular catheters are disclosed in US patent publication Nos. 2015/0112195 to Berger et al., and 2018/0116704 to Ryba et al., the disclosures of each of which are hereby expressly incorporated by reference in their entireties herein.

Referring to FIG. 7G, there is illustrated a cross section through a distal stopper 2414 in which the slider 441 is a continuous circumferential wall having a continuous peripheral bearing surface 442. Three struts 440 are spaced apart to define three flow passageways 443 extending axially therethrough. The sum of the surface areas of the leading edges of the struts 440 is preferably minimized as a percentage of the sum of the surface areas of the open flow passageways 443. This allows maximum area for aspiration while still providing adequate support axially for the distal surface 446 (see FIG. 7F) to engage the complementary stop surface on the inside wall of the catheter and prevent the tip 2416 from advancing distally beyond a preset relationship with the catheter. The sum of the leading (distal facing) surface area of the struts is generally less than about 45% and typically is less than about 30% or 25% or 20% of the sum of the areas of the flow passageways 443.

In an embodiment having a torque coil 2412 with an OD of about 0.028 inches, the OD of the stopper 2414 is about 0.068 inches. The wall thickness of the struts is generally less than about 0.015 inches and typically less than about 0.010 inches and in some implementations less than about 0.008 inches or 0.005 inches or less. The struts 440 have a length in the catheter axial direction that is sufficient to support the assembly against distal travel beyond the catheter stop ring, and may be at least about 50% of the OD of the stopper 2414. In a stopper 2414 having an OD of about 0.68 inches, the struts 2440 have an axial length of at least about 0.75 mm or 0.95 mm.

Referring to FIG. 7H, there is illustrated a stopper 2414 having three distinct sliders 441 each supported by a unique strut 440. The sum of the circumference of the three peripheral surfaces is preferably no more than about 75% and in some implementations no more than about 50% or 40% of the full circumference of a continuous circumferential peripheral surface 442 as in FIG. 7G. This further increases the cross sectional area of the flow paths 443. In a catheter having an ID of no more than about 0.07 inches, an OD of the hub 443 of at least about 0.026 or 0.028 or 0.030 or more, the sum of the flow paths 443 is at least about 0.0015 inches, and preferably at least about 0.020 or 0.022 inches or more. The area of the leading edges of the struts 440 and sliders 441 is preferably less than about 0.003 inches, and preferably less than about 0.001 inches or 0.0008 inches or less. In the catheter axial direction, the length of the struts 440 is at least about 0.50 mm or 0.75 mm, and in one embodiment the length of the struts 440 and sliders 441 is about 1 mm.

Referring to FIG. 8A, a modified distal tip 50 includes a helical thread 52 extending from a distal tip 54 to a proximal end 56 and supported by a core wire 58. The axial length of the distal tip 50 is at least about 2 mm or 5 mm or 10 mm and in some embodiments no more than about 30 mm or 20 mm measured along the core wire 58. The helical thread 52 wraps around the axis at least about 1 or 2 or 4 or more full revolutions, but in some embodiments no more than about 10 or 6 revolutions. In some embodiments the axial length along the threaded portion of the tip is within the range of from about 1 to about 8 revolutions.

The helical thread 52 on this implementation may have a constant pitch throughout its length. The pitch may be within the range of from about 10 to about 20 threads per inch, or about 5 to about 10 threads per inch depending upon desired performance. Alternatively, the thread may have multiple pitches designed to engage, transport and grasp thrombus within the catheter lumen. A distal pitch may be less than a proximal pitch. The pitch may vary continuously along the length of the thread, or may step from a first, constant pitch in a proximal zone to a second, different pitch in a distal zone of the thread. The thread 52 may comprise a continuous single helical flange, or may have a plurality of discontinuities to produce a plurality of teeth or serrations, arranged helically around the core wire.

The side elevational profile or envelope scribed by the distal tip as it rotates may have a linear or nonlinear taper on one or both ends which provide varying diameter and thus clearance along its length from the generally cylindrical ID of the catheter lumen. The maximum outer diameter 60 of the envelope (Max OD) is defined by the major diameter of the thread, and the tapers may be optimized for improved thrombus engagement and/or thrombus clearance as the helical thread element is rotated in the catheter.

Referring to FIG. 8A, the Max OD 60 in a first zone may be up to the diameter of a sliding fit within the catheter lumen, and may generally be at least about 0.015 inches or 0.010 inches smaller than the catheter lumen ID. In some implementations, the Max OD of the tip may be significantly less than the inside diameter of the catheter lumen to allow more space for the thrombus, but still create significant grasping force via engagement of the helical threads with the thrombus. In one implementation, the maximum helical thread diameter is about 0.110 inches and the catheter lumen ID is about 0.275 inches (24 F) (a 0.165 inch gap between the helical threads and catheter wall.

In the illustrated embodiment, the side elevational view profile of the helical thread OD tapers down in a proximal direction in a second zone, and tapers down in a distal direction in a third zone, such that the Max OD occurs with the central 30% or 20% or 10% of the axial length between distal tip 54 and proximal end 56.

The radial depth of the threads from the core 58 (minor diameter) to the outermost free edge 53 of the thread elements (major diameter) can be varied by varying either the major diameter as described above, as well as by varying the minor diameter (by varying the diameter of the core). The core may have a constant diameter throughout its length, or may taper, typically smaller in the distal direction as seen in FIG. 8.

The profile of the tip 50 viewed along the axis of rotation may be circular, or may vary to create a non circular pattern around the axis of rotation as seen in FIG. 9. The tip as seen in an end elevational view thus exhibits a major diameter 62 and a minor diameter 64. The minor diameter may be no more than about 95% or 90% or 80% or 70% of the major diameter, depending upon desired performance.

In certain applications, the Max OD of the tip is no more than about 35% or about 50% or about 60% of the ID of the catheter, to leave a substantial tip bypass flow path. Since this implementation does not have any centering structures, the tip will normally be pushed to one side of the aspiration lumen. When a clot becomes lodged between the tip and the opposing wall of the catheter, manual rotation of the tip can engage the clot like a worm gear and either grasp the clot (e.g., by pinning it against the opposing catheter sidewall) for retraction or facilitate freeing the blockage and aid in ingestion of the clot into the catheter.

A variation of the distal tip 50 is illustrated in FIGS. 8B and 8C. The illustrated tip 50 includes a distal advance segment 55 extending between an atraumatic distal tip at 54 and a transition 57. Helical thread 52 extends proximally from transition 57 to a proximal end 56 of the helical thread 52. A trailing segment 59 extends between the proximal end 56 of the thread and the proximal end of the tip. The thread may be inclined in a proximal direction, to produce a proximally facing undercut and a distal surface that inclines radially outwardly in a proximal direction.

The axial length of the advance segment 55 may be at least about 1 cm or 2 cm and in some implementations is within the range of from about 2 cm to about 4 cm. The axial length of the helical thread 52 along the longitudinal axis is typically within the range of from about 1 cm to about 5 cm and in certain implementations between about 2 cm and 3 cm.

The outside diameter of the advance segment 55 at distal tip 54 is generally less than about 0.024 inches, or less than about 0.020 inches and, in one implementation, is about 0.018 inches. The maximum outside diameter of the advance segment 55 and helical thread 52 may be within the range from about 0.020 to about 0.050 inches, and, in one implementation, is less than about 0.040 inches, such as about 0.035 inches. The advance segment, helical thread and trailing segment of the tip 50 may be molded over the core wire 58 using any of a variety of polymers known in the catheter arts.

Referring to FIG. 8C, a first radiopaque marker 63 may be carried on the core wire 58 beneath the advance segment 55. A second radiopaque marker 65 may be carried on the core wire 58 within the trailing segment 59. Each radiopaque marker may comprise a coil of radiopaque wire such as a platinum iridium alloy wire having a diameter about 0.002 inches, and wrapped around the core wire 58 and soldered to the core wire 58 to produce an RO coil having an outside coil diameter of less than about 0.020 inches, such as about 0.012 inches. The radiopaque markers may also function as an axial interference fit between the core wire 58 and the molded advance segment 55 and trailing segment 59 to resist core wire pull out from the tip 50.

In one implementation, the maximum OD of the thread 52 exceeds the maximum OD of the advance segment 55 by at least about 15% or 25% or 30% or more of the OD of the advance segment 55, to facilitate crossing the clot with the advance segment 55 and engaging the clot with the thread. The thread pitch may be within the range of from about 0.75 to about 0.30, or within the range of from about 0.10 and about 0.20, such as about 0.14 inches.

Preferably, the maximum OD of the tip 50 is less than about 60% or 50% of the aspiration catheter ID, and may be within the range of from about 35% to about 55% of the catheter ID. In certain implementations, the maximum OD of the tip 50 may be within the range of from about 0.044 inches to about 0.050 inches within a catheter having an ID within the range from about 0.068 inches to about 0.073 inches.

For this configuration of the tip 50, the distal stop on the proximal end of the core wire 58 is configured to permit distal advance of the tip 50 such that the distal end 54 may be advanced at least about 2 to 3 cm and preferably as much as 4 to 8 cm beyond the distal end of the catheter. In one implementation, the distal stop limits distal advance of the tip 50 so that the proximal end is within two or within one or than 0.5 cm in either the distal or proximal direction from the distal end of the aspiration catheter.

Referring to FIG. 10, the helical tip element may be part of an over-the-wire structure which can be moved over a guide wire. This structure allows the guide wire to be positioned and the helical tipped structure can be inserted with a surrounding catheter, or independently into a surrounding catheter which is already in place and over the guidewire. The helical tip structure can be rotated freely around the guide wire. The lumen 66 may be used for a guide wire or other devices or fluids to communicate from proximal end of the torque member through the distal tip of the helical tip element.

FIG. 11 illustrates one embodiment of an over-the-wire helical tipped engagement wire 46 with a central lumen having guidewire 70 extending therethrough. Similar to other helical tip structures disclosed therein, this is intended to operate within a coaxial surrounding catheter as has been previously discussed. As with implementations discussed elsewhere herein, engagement wire 46 includes an elongate flexible body configured to transmit torque between a proximal hub or handle 70 and the distal tip 50. The body may comprise a torque coil construction as disclosed elsewhere herein, having two or more concentric coils typically wound in a reverse direction from the adjacent coil. The engagement wire 46 optionally includes an axially extending longitudinal stabilizer 82. Preferably, the torque coil is enclosed within a polymeric jacket such as a shrink wrap tube.

The helical tip may alternatively have a fixed guide wire 72 distal advance segment extending from the distal end of the helical tip (See FIG. 12) or a polymeric distal extension to provide an atraumatic tip (See FIG. 8B). This fixed guide wire advance segment is typically easily bent when interacting with the patient's anatomy to avoid injuring tissue. The fixed guide wire advance segment may be between about 1 cm and about 10 cm but may be shorter or longer depending on the application.

In accordance with another aspect of the invention, a catheter dilator sheath assembly is provided to enable easy, safe, and efficient tracking of a large diameter catheter or catheter system from insertion into a large peripheral blood vessel and advanced to the target location of interest. The large diameter catheter, such as for aspiration or other mechanical means of removal of embolus or thrombus from large vessels, has a diameter within the range from about 8 F (0.105″) to about 24 F (0.315″).

Referring to FIGS. 6 and 13, one implementation of the catheter 60 includes an elongate flexible tubular body 50, having a proximal end 52, a distal end 54 and a side wall 56 defining a central lumen 58. Referring to FIG. 14, an elongate flexible cannulated rail or dilator 61 is shown extending over the guidewire 70 and occupying the space between the guidewire 70 and the large inside diameter of the central lumen 58 of the large diameter catheter 60 to provide support to the catheter and/or an atraumatic tip during delivery.

This catheter-cannulated rail-guidewire assembly is intended to easily track through anatomical challenges more easily than the catheter. The catheter-rail-guidewire assembly then acts as a first stage of the catheter delivery system and enables the large diameter catheter or catheter system to be inserted and independently advanced over this first stage into a blood vessel (e.g. the femoral vein) percutaneously over a guidewire and advanced through potentially tortuous vasculature to the remote target location of interest without requiring advanced skills or causing kinking of the catheter.

The cannulated rail 61 may comprise a soft flexible cylindrical body having a guidewire lumen with a diameter of no more than about 0.040″ and an outside diameter no greater than about 0.025″ or about 0.010″ smaller than the inner diameter of the large diameter catheter. Thus the wall thickness of the cannulated rail 61 is typically at least about 0.010″ less than the radius of the large diameter catheter and in some implementations at least about 0.120″ or more, depending upon the size of the annular space between the inside diameter of the catheter and the outside diameter of the guidewire. Depending upon the ID of the access catheter, the rail 61 may have a wall thickness of at least about 0.05 inches, at least about 0.075 inches, at least about 0.100 inches and in some implementations at least about 0.12 inches. The wall thickness of the rail may exceed the inside diameter of the guidewire lumen.

The cannulated rail 61 may have an elongated advance segment having a tapered distal tip 62 that may project beyond the distal end 54 of the catheter 60. The thick sidewall of the cannulated rail 61 may comprise one or more flexible polymers, and may have one or more embedded column strength enhancing features such as axially extending wires, metal or polymeric woven or braided sleeve or a metal tube, depending upon the desired pushability and tracking performance along the length of the dilator.

Optionally, the proximal segment of the rail or dilator which is not intended to extend out of the distal end of the catheter may be a structure which is not coaxial with the guidewire, but is instead a control wire which extends alongside the guidewire in the catheter and allows the distal tubular telescoping segment of the rail or dilator to be retracted or extended. (analogous to rapid exchange catheters) without the entire length of the rail structure being over the wire. This allows removal or insertion of the rail or dilator over a shorter guidewire because of the shorter coaxial segment tracking over the guidewire. The distal tubular segment may have a length of no more than about 40 cm or 30 cm or less, carried by a proximally extending control wire.

Catheter 60 may be provided with a proximal hub 120, having a port for axially movably receiving the rail 61 therethrough. The hub 120 may be provided with an engagement structure such as a first connector 122 for releasably engaging a second complementary connector 124 on a hub 126 on the proximal end of the rail 61. First connector 122 may comprise an interference structure such as at least one radially moveable projection 130, for releasably engaging a complementary engagement structure such as a recess 132 (e.g., an annular ridge or groove) on the hub 126. Distal advance of the rail 61 into the catheter 60 causes the projection 130 to snap fit into the recess 132, axially locking the catheter 60 and rail 61 together so that they may be manipulated as a unit.

The dilator is inserted through the hemostasis valve in the hub 120 of a large bore (e.g., 24 F) catheter 60 and advanced through the catheter until the retention clip on the dilator hub 126 or catheter hub 120 snaps into the complementary recess on the other hub. In this engaged configuration, the flexible distal end of the 24 F rail dilator 61 will extend at least about 5 cm or 10 cm, and in some implementations at least about 15 cm or 20 cm beyond the distal end 54 of the 24 F catheter 60. The rail dilator and 24 F catheter system are thereafter distally advanced over a previously placed guidewire and into the introducer sheath.

The dilator and catheter combination of the present invention differentiate over prior systems both because of the flexibility of a distal zone of the dilator and greater length of the dilator than the corresponding catheter. Typically, a dilator is a uniform stiffness and length-matched to its catheter, with only a short atraumatic tip of the dilator extending beyond the distal end of the catheter. The dilator of the present invention has a supportive proximal end and a flexible distal end, with a total dilator length much longer than the catheter 60 to enable, as an example, the following procedure.

In use, a guidewire 70 such as an 0.035″ guidewire is advanced under fluoroscopy using conventional techniques into a selected vessel. The cannulated rail 61, optionally with the catheter 60 mounted thereon, is loaded over the proximal end of the guidewire 70 and advanced distally over the wire until the distal end of the rail is in position at the target site.

The 24 F catheter 60 is thereafter unlocked from the rail 61 and advanced over the rail 61 to the desired site, supported by the rail 61 and guidewire 70 combination. Because the uncovered advance section of the rail has already traversed the challenging tortuosity through the heart, the catheter 61 now just slides over the advance section of the rail for easy passage to the final target location. The supportive proximal zone and flexible distal advance section of the rail enables ease of delivery through the most challenging anatomy in, for example, a PE procedure going from the vena cava through the tricuspid and pulmonary valves of the heart into the central pulmonary artery without concern about damaging the tissue (atraumatic, flexible tip) or damaging the dilator (high kink resistance due to flexible, high wall thickness “solid” dilator construction.

The cannulated rail 61, or the cannulated rail 61 and the guidewire 70 combination, may thereafter be proximally withdrawn, leaving the large bore catheter 60 in position to direct a procedure catheter such as any of the aspiration catheters disclosed elsewhere herein to the target site.

Referring to FIG. 15, the large diameter (LD) catheter 60 may in some situations have a smaller diameter (SD) catheter though its central lumen for the purposes of introducing an additional functionality (e.g., clot grabber catheter 62, imaging catheter 10, or mechanical thrombectomy tool 66) and/or telescoping the SD catheter to more distal locations in the anatomy. In order to enable delivery of the LD catheter 60 and SD catheter as a single system, the SD catheter may have a core dilator 68 for support, and the gap between the outer diameter of the SD catheter and inner diameter of the LD catheter 60 may be maintained or supported by a second, tubular dilator 71. The tubular dilator 71 may have a shaped distal tip 72 for a smooth tapered transition from the SD catheter 41 to the LD catheter 40. The distal end 34 of the core dilator may be provided with a complementary taper to the distal taper of the thin wall SD dilator (FIG. 16) or may end at the distal end of the LD catheter (FIG. 17).

The core dilator 68 inside the SD catheter 41 and tubular dilator 70 between the two catheters may have an interlocking feature to create a single (SD+LD) catheter+(core+tubular) dilator system. For example, complementary connectors may be provided on hubs on the proximal ends of the system components.

Referring to FIG. 17, the tip of the tubular dilator 70 may be configured to taper to the guidewire lumen 76, thus covering and extending distally beyond the small diameter catheter 41 if it is in place. The tip of the tubular dilator 70 may be provided with a longitudinally extending slit 78, scored or perforated one or more times to allow the tip to split longitudinally and be pulled back into the space between the LD and SD catheters and fully expose the distal end of the small diameter catheter 41. See FIG. 18.

The single (SD+LD) catheter+(core+tubular) dilator system may be pre-assembled and detachably interlocked at the proximal hub. Additional tubular dilators having a series of outside diameters and wall thicknesses may be provided such that the SD catheter may be used in combination with different diameter LD catheters. A LD catheter may be used with different SD catheters by providing tubular dilators having the same OD but a series of different inside diameters. The core+tubular dilators may simply be pulled proximally to withdraw both dilators as a single system, or the tubular dilator may be configured with a tab or handle at the proximal end and a slit, scoring, perforation or other mechanism so as to split, peel, or tear it along the longitudinal axis during withdrawal to allow the tubular dilator to peel from the SD catheter as it slides proximally out of the space between the LD and SD catheters. (FIG. 18)

Any of the thrombectomy catheters disclosed herein may be provided with a surface configuration on the inside surface of the central lumen to affect the behavior of clot drawn into the lumen. In general, the catheter, with diameter within the range from about 8F (0.105″) to about 24 F (0.315″), includes an elongate flexible tubular body, having a proximal end, a distal end and a side wall defining a central lumen. The access or evacuation catheters may also include a rotatable core wire or other apparatus that extends though the catheter lumen for the purposes of engaging thrombus at the distal end of the catheter as has been discussed.

The central lumen 90 is defined by an inside surface 100 of the tubular body 104, which in some embodiments is a smooth cylindrical surface. However, referring to FIGS. 19A and 19B, the inner surface 100 of at least a distal zone 102 of the tubular body 104 may be provided with a surface configuration to engage thrombus and limit unrestricted sliding of the thrombus along the inner surface 100. The distal zone 102 may have an axial length within the range of from about 0.5″ to about 12″ or more, depending upon desired performance and/or manufacturing technique.

For example, referring to FIG. 19A, at least one or five or ten or more axially extending surface structures such as radially inwardly extending ridges 106 separated by grooves 108 may be provided to facilitate proximal ingestion of the thrombus and/or to engage thrombus and resist rotation of the thrombus within the lumen when the core wire or other thrombus grabbing apparatus is rotated within the lumen.

The corrugation pattern may also increase the transport of the thrombus proximally by decreasing the surface area of contact between the thrombus and the inside surface of the tubular body. The spacing circumferentially may be regular or irregular, and the crest and trough pattern, dimensions and distribution may be varied. Examples of trough cross sections include the illustrated rectangular, semicircular or triangular, among others.

In one implementation illustrated in FIG. 19B, the surface discontinuity, i.e. grooves or ridges, may extend in a circumferential (e.g. helical) configuration having a constant or variable pitch along the length of the distal zone 102. The helical guide may spiral in a first direction in order to oppose rotation of the core wire or other apparatus in a second direction, or in the same direction to cooperate with the rotation of the core wire in order to facilitate thrombus ingestion proximally into the catheter. The grooves or ridges may have a curved profile or generally rectilinear, having generally flat or cylindrical side walls.

In another embodiment, the inner surface 100 of the distal zone 102 of the tubular body 104 may have a three-dimensional pattern that reduce friction of the thrombus moving proximally in the catheter and create resistance to the thrombus moving distally in the catheter after it has been ingested into the catheter. This pattern may be regular throughout or in the distal end of the tubular body, or irregular and decrease gradually and progressively in density, pattern, or geometry along the length of the catheter or the distal section. This pattern may also be provided in combination with lubricious coatings or surfaces.

The three-dimensional differential friction pattern may be defined by a regular or irregular pattern of protuberances 110 or depressions on the inner surface of the catheter, each of which presents an exposed face 112 inclined radially inwardly in the proximal direction, with each inclined exposed face 112 terminating proximally in a proximally facing engagement surface such as a dropoff edge 114, which may be curved in an axial direction as shown in FIG. 21 to provide a ratchet or fish scale type of configuration.

The scales may flex, hinge or pivot at the distal end, which will not impact the proximal ingestion of the thrombus, but will create additional resistance to the thrombus moving distally in the catheter after it has been ingested into the catheter.

In alternative embodiments, the differential friction surface structures on the inner surface of the distal zone may be relatively shallow convex or concave “dimples” or other regular or irregular surface discontinuities that are generally triangular, oval, oblong arcs, serpentine shapes or a plurality of angled fibers that incline radially inwardly in a proximal direction.

Referring to FIG. 22, the lumen 116 of the tubular body may be non-cylindrical and instead be oval or other geometry lacking rotational symmetry and containing a minor axis which is less than a major axis due to one or more longitudinal deformations of the lumen. These longitudinal deformations of at least the inner surface of the tubular body serve as structures to increase the rotational resistance to thrombus or embolic matter in the lumen. These deformations may contain their own lumens within the wall of the tubular body for pull wires of a steerable tip or to deliver fluids or to measure pressure or to transmit a vacuum or other functions.

The distal end 118 of the tubular body may be angled such that the distal face of the catheter resides on a plane or a curve with an end to end secant that crosses the longitudinal axis of the tubular body at an angle within the range from about 30 degrees to about 60 degrees. The distal face of the angled tip may be non-planar and may include one or two or more inflection points or curves. This angled tip may improve catheter navigation and thrombus ingestion by providing more surface area for engagement between the catheter and the thrombus. (see, e.g., FIG. 31D and associated description in US publication No. 2020/0001046 A1 to Yang, et al., which is hereby incorporated in its entirety herein by reference.)

The opening at the distal end of the tubular body may be expandable from a first inside diameter for transluminal navigation to a second, larger inside diameter providing a funnel like tip with an enlarged distal opening to facilitate aspiration of thrombus into the lumen. The diameter at the distal opening of the fully open funnel exceeds the diameter of the cylindrical distal end of the tubular body by at least about 5% or 10% or more. (see FIGS. 4A-41 and associated description in U.S. Pat. No. 10,441,745 to Yang, et al., which is hereby incorporated in its entirety herein by reference.)

The distal end of the catheter may have an increasing inner diameter while maintaining a constant outer diameter, representing a tapered distal wall, or the inner and outer diameters may both increase, representing a conical funnel like tip.

The funnel tip is may be made of a material that is rigid enough to maintain structural integrity under aspiration and flexible enough that it may deform to accommodate and enable thrombus across a range of size, shape, and maturity to be aspirated into the catheter lumen.

The funnel tip may telescope out of the thrombectomy catheter. A hollow cylindrical structure at the end of a long, flexible hypo tube or at the end of two or more stiff wires may be advanced through the catheter, and when the hollow cylindrical structure extends beyond the distal catheter tip and its associated circumferential constraint, the structure expands into a conical funnel shape. Additional details of these features may be found in U.S. Pat. No. 10,441,745 to Yang, et al., previously incorporated in its entirety herein by reference.)

The thrombectomy catheter with inner lumen features to enhance the extraction of thrombus and/or distal end features may enable easier, more efficient removal of a broad spectrum of thrombus size, shapes, and maturity from vascular conduits including the pulmonary arteries, resulting in shorter procedure times and a lower total volume of blood loss. This is achieved by promoting proximal movement of the thrombus while creating resistance to the thrombus moving distally in the catheter after it has been ingested into the distal catheter.

The foregoing inventions and improvements will enable the engagement and capture of a very wide range of thrombus, from acute to mature in nature, thus enabling the extraction of the thrombus from the blood vessel in which it may be impeding blood flow. Additionally, the configurations described above enhance safety by reducing the risk of vascular tissue injury due to mechanical engagement of the helical tip element and/or catheter tip with the vessel wall.

In the foregoing description, similar features in different drawings are sometimes identified by slightly differing terminology. This is not intended to imply differences that do not exist. Slightly different features are illustrated in different drawings, and those of skill in the art will recognize that any of the features disclosed here in can be re-combined with any of the catheters or other structures disclosed here in. 

What is claimed is:
 1. A method of removing foreign material from the vascular system, comprising the steps of: positioning the distal tip of a sensing catheter in proximity to a target foreign material; propagating a signal from the sensing catheter; receiving a return signal; and capturing and removing at least a portion of the foreign material when the return signal is indicative of a foreign material located within a capture zone.
 2. A method of removing foreign material as in claim 1, wherein the capturing and removing steps are accomplished by the sensing catheter.
 3. A method of removing foreign material as in claim 1, further comprising removing the sensing catheter following the receiving a return signal step, and introducing a clot capture catheter to accomplish the capturing and removing steps.
 4. A method of removing foreign material as in claim 1, wherein the foreign material is a clot.
 5. A method of removing foreign material as in claim 4, wherein the clot is located in the venous system.
 6. A method of removing foreign material as in claim 5, wherein the foreign material is a deep vein thrombosis.
 7. A method of removing foreign material as in claim 5, wherein the foreign material is a pulmonary embolism.
 8. A method of removing foreign material as in claim 1, wherein the return signal enables characterization of tissue within the capture zone.
 9. A method of removing foreign material as in claim 8, wherein the return signal enables differentiation between clot and vessel wall within the capture zone.
 10. A method of removing foreign material as in claim 1, wherein the propagating a signal step comprises propagating an ultrasound signal.
 11. A method of removing foreign material as in claim 1, wherein the propagating a signal step comprises propagating an electromagnetic signal.
 12. A method of removing foreign material as in claim 11, wherein the electromagnetic signal is in the UV-visible range.
 13. A method of removing foreign material as in claim 1, wherein the electromagnetic signal comprises multiple wavelengths.
 14. A method of removing foreign material as in claim 9, further comprising the step of deflecting the tip laterally in response to detecting vessel wall within the capture zone, prior to the capturing and removing steps.
 15. A method of removing foreign material as in claim 1, wherein the propagating a signal step comprises propagating visible light through the sensing catheter and beyond the distal tip.
 16. A method of removing foreign material as in claim 15, further comprising receiving the return signal using a sensor carried by the sensing catheter.
 17. A method of removing foreign material as in claim 16, further comprising the step of creating a visible light pathway through blood between the distal tip and the target foreign material.
 18. A method of removing foreign material as in claim 17, wherein the step of creating a visible light pathway through blood between the distal tip and the target foreign material comprises infusing an optically transparent medium to displace blood from the pathway.
 19. A method of removing foreign material as in claim 18, further comprising the step of deploying a barrier to temporarily contain at least a portion of the optically transparent medium within the pathway.
 20. A method of removing foreign material as in claim 9, wherein the differentiation is accomplished by a clinician, observing an image generated by the return signal.
 21. A method of removing foreign material as in claim 9, wherein the differentiation is accomplished by a processor configured to differentiate between return signals indicative of either a foreign material or a vessel wall.
 22. A method of removing foreign material as in claim 21, wherein the processor is further configured to generate an indicium in response to the differentiation between a foreign material and a vessel wall.
 23. A dual dilator access system, comprising: a large diameter access catheter, having an elongate tubular body with a proximal end, a distal end and a central lumen extending axially therethrough; a small diameter catheter axially movably slidable through the central lumen; a first dilator extendable through the central lumen, in between the small diameter catheter and the large diameter catheter; and a second dilator extendable through the small diameter catheter.
 24. A system as in claim 23, wherein the large diameter catheter is an aspiration catheter.
 25. A system as in claim 24, wherein the small diameter catheter is a clot grabber catheter.
 26. A system as in claim 23, further comprising a proximal coupling for interlocking the large diameter catheter and the small diameter catheter.
 27. A system as in claim 23, wherein the first dilator has a tapered distal end.
 28. A system as in claim 23, wherein the large diameter access catheter is at least about 14 French.
 29. A system as in claim 25, wherein the clot grabber catheter includes a distal tip with a helical thread.
 30. A system as in claim 23, wherein the small diameter catheter comprises an imaging catheter.
 31. A system as in claim 23, wherein the first dilator has a split line along which it can split for proximal retraction and removal. 